1. Chapter 2
The X-ray Beam

2. X-ray production requires three things
Lots of electrons Give electrons kinetic energy Convert electron kinetic energy into electromagnetic energy (x-rays)

3. X-ray machine
X-ray machine is an electrical / mechanical device which converts energy from one form into another

4. X-ray Production
The production of x-rays requires a rapidly moving stream of electrons that are suddenly decelerated or stopped.
The negative electrode (cathode) is heated, and electrons are emitted (thermionic emission).
The electrons are attracted to the anode, move rapidly towards the positive electrode, and are stopped or decelerated.

5. tube housing

6. X-ray Tube Housing Metal or glass envelope
Negatively charged electrode
Positively charged electrode

7. Cathode Filament Source of electrons Coiled tungsten wire Focusing cup
Filament current
Thermionic emission
Coiled tungsten wire
Large and small
Focusing cup
Space charge effect

8. Anode Rotating anode Target Requires a stator and rotor to rotate
Tungsten metal
High melting point
Efficient x-ray production
Target
Decelerates and stops electrons
Energy converted to heat and x-rays
Bremsstrahlung and characteristic interactions

9. Target Interactions Bremsstrahlung interactions
Braking or slowing down radiation
85% of x-ray beam
Characteristic interactions
Projectile electron energy at least 69.5 keV
Inner shell electron ionized
15% of x-ray beam
X-ray properties the same

10. Target Interactions (cont.)

11. X-ray Exposure

12. X-ray Exposure (cont.)

13. X-ray Emission Spectrum
The range and intensity of x-rays emitted changes with different exposure technique settings on the control panel.

14. X-ray Beam Quantity and Quality
Quantity: number of x-ray photons in primary beam
Quality: penetrating power of x-ray beam
Kilovoltage
Milliamperage
Exposure time

15. Kilovoltage Creates potential difference
Determines the speed of the electrons in tube current
Greater speed results in greater quantity and quality of primary beam
Increasing electron speed will increase x-ray beam penetrability

16. Milliamperage
Unit to measure tube current or number of electrons flowing per unit time
mA directly proportional to quantity of x-rays produced
Double the mA will double the number of x-ray photons produced

17. Milliamperage and Time
Exposure time determines the length of time x-rays are produced.
Increasing time will increase the total number of x-rays produced.
Exposure time and x-ray quantity are directly proportional.

18. Milliamperage and Time (cont.)
Milliamperage × time = mAs
200 mA × 0.25 s = 50 mAs
400 mA × 0.25 s = 100 mAs
200 mA × 0.50 s = 100 mAs
Changing the mA or time will change the quantity of x-rays produced.

19. Three things to have usable x-rays

20. X-rays must come from as close to a point source as possible X-rays must travel in straight lines X-rays must create contrast

21. Why can’t x-rays come from a point source??????

22. Line Focus Principle
Relationship between actual and effective focal spot
Actual focal spot: area on anode target exposed to tube current electrons
Effective focal spot: focal spot size as measured directly under anode target
The smaller the anode angle the smaller the effective focal spot size

23. Anode Heel Effect
X-rays are more intense on the cathode side of the x-ray tube.
The intensity of the x-rays decrease toward the anode.
Place the thicker anatomic area under the cathode end for more even exposure to the image receptor.

24. filtration

25. Heat Units
During x-ray production, most of the electron kinetic energy is converted to heat and can damage the x-ray tube.
Heat units (HU) = mA × time × kVp × generator factor

26. Extending X-ray Tube Life
If applicable, warm up tube.
Avoid excessive heat generation.
Do not hold down rotor button without making exposure.
Use lower mA and longer exposure time.
Don’t move tube while energized.
Recognize unusual noises, and report.